2011 Particle Accelerator Conference - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
MOP042	Design of a Superconducting Photonic Band Gap Structure Cell	SRF, cavity, HOM, wakefield	178
	E.I. Simakov LANL, Los Alamos, New Mexico, USA C.H. Boulware, T.L. Grimm Niowave, Inc., Lansing, Michigan, USA
	Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program. We present a design of a superconducting photonic band gap (PBG) accelerator cell operating at 700 MHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. Using PBG structures in superconducting particle accelerators will allow moving forward to significantly higher beam luminosities and lead towards a completely new generation of colliders for high energy physics. We designed the superconducting PBG cell which incorporates higher order mode (HOM) couplers to conduct the HOMs filtered by the PBG structure out of the cryostat. The accelerator characteristics of the cell were evaluated numerically. A scaled prototype cell was fabricated out of copper at the higher frequency of 2.8 GHz and cold-tested. The 700 MHz niobium cell will be fabricated at Niowave, Inc. and tested for high gradient at Los Alamos in the near future.

TUP032	Development of 1.3 GHz Prototype Niobium Single Cell Superconducting Cavity Under IIFC Collaboration	cavity, vacuum, controls, electron	871
	A. Puntambekar, M. Bagre, J. Dwivedi, P.D. Gupta, R.K. Gupta, S.C. Joshi, G.V. Kane, R.S. Sandha, S.D. Sharma, P. Shrivastava RRCAT, Indore (M.P.), India C.A. Cooper, M.H. Foley, T.N. Khabiboulline, C.S. Mishra, J.P. Ozelis, A.M. Rowe, G. Wu Fermilab, Batavia, USA V. Jain IIT, Mumbai, India D. Kanjilal, K.K. Mistri, P.N. Potukuchi, J. Sacharias IUAC, New Delhi, India V.C. Sahni Homi Bhbha National Institute (HBNI), DAE, Mumbai, India
	Under Indian Institutions Fermilab collaboration (IIFC), Raja Ramanna Centre for Advanced Technology (RRCAT) Indore, Inter University Accelerator Centre (IUAC) New Delhi and Fermi National Accelerator Laboratory (FNAL) have developed two prototype 1.3 GHz niobium single cell superconducting cavities. Development of forming tools, forming of half cells, machining of components, development of welding fixtures along with RF & vacuum qualification were carried out at RRCAT. The electron beam welding was carried out at IUAC. The fabricated prototype cavities were tested for RF and vacuum leak tightness up to 77 K at RRCAT before shipment to FNAL. Processing, consisting of CBP, EP, and heat treatment was carried out jointly by FNAL and Argonne National Laboratory in USA. Both the prototype cavities were tested at 2 K in the VTS facility at FNAL and have achieved the accelerating gradient of ~ 19 to 21 MV/m with Q > 1.5 ·10⁺¹⁰. This paper will report the developmental efforts carried out in tooling, forming, machining, welding & various qualification procedures adopted. The paper will also present the processing and the 2 K test results.

TUP046	Superconducting 72 MHz β=0.077 Quarter-wave Cavity for ATLAS	cavity, linac, ion, cathode	892
	M.P. Kelly, Z.A. Conway, S.M. Gerbick, M. Kedzie, R.C. Murphy, P.N. Ostroumov, T. Reid ANL, Argonne, USA
	A 72 MHz superconducting (SC) niobium quarter-wave cavity (QWR) optimized for β=0.077 has been built and tested as part of a beam intensity upgrade of the ATLAS SC heavy-ion linac. The two-gap cavity, designed to accelerate ions over the velocity range 0.06<β<0.12 and provide 2.5 MV of accelerating voltage per cavity at T=4.5 Kelvin, is based on a highly optimized electromagnetic design to reduce surface electric and magnetic fields. Horizontal electropolishing on the complete cavity with the helium jacket, is similar to that performed on 1.3 GHz ILC-type cavities and is a first for a low-β TEM cavity. This development is part of a broader effort to demonstrate ~120 mT surface fields with Rs~5 nΩ in 2 K operation for low-β cavities with the aim of substantially reducing the footprint for future ion linacs. First rf cold test results show the highest accelerating gradients (13.4 MV/m, leff=βλ) and voltage/cavity (4.3 MV) achieved for this class of SC cavity.

TUP054	Mechanical Design of 56 MHz Superconducting RF Cavity for RHIC Collider	cavity, SRF, vacuum, resonance	907
	C. Pai, I. Ben-Zvi, A. Burrill, X. Chang, G.T. McIntyre, R. Than, J.E. Tuozzolo, Q. Wu BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. A 56 MHz Superconducting RF Cavity operating at 4.4K is being constructed for the RHIC collider. This cavity is a quarter wave resonator with beam transmission along the centreline. This cavity will increase collision luminosity by providing a large longitudinal bucket for stored bunches of RHIC ion beam. The major components of this assembly are the niobium cavity with the mechanical tuner, its titanium helium vessel and vacuum cryostat, the support system, and the ports for HOM and fundamental dampers. The cavity and its helium vessel must meet the ASME pressure vessel code and it must not be sensitive to frequency shift due to pressure fluctuations from the helium supply system. Frequency tuning achieved by a two stage mechanical tuner is required to meet performance parameters. This tuner mechanism pushes and pulls the tuning plate in the gap of niobium cavity. The tuner mechanism has two separate drive systems to provide both coarse and fine tuning capabilities. This paper discusses the design detail and how the design requirements are met.

TUP055	Design and Preliminary Test of the 1500 MHz NSLS-II Passive Superconducting RF Cavity	cavity, HOM, cryomodule, vacuum	910
	J. Rose, W.K. Gash, B.N. Kosciuk, V. Ravindranath, S.K. Sharma, R. Sikora, N.A. Towne BNL, Upton, Long Island, New York, USA C.H. Boulware, T.L. Grimm, C. Krizmanich, B. Kuhlman, N. Miller, B. Siegel, M.J. Winowski Niowave, Inc., Lansing, Michigan, USA
	NSLS-II is a new ultra-bright 3 GeV 3rd generation synchrotron radiation light source. The performance goals require operation with a beam current of 500mA and a bunch current of at least 0.5mA. Ion clearing gaps are required to suppress ion effects on the beam. The natural bunch length of 3mm is planned to be lengthened by means of a third harmonic cavity in order to increase the Touschek limited lifetime. Earlier work described the design alternatives and the geometry selected for a copper prototype. We subsequently have iterated the design to lower the R/Q of the cavity and to increase the diameter of the beam pipe ferrite HOM dampers to reduce the wakefield heating. A niobium cavity and full cryomodule including LN2 shield, magnetic shield and insulating vacuum vessel have been fabricated and installed.

TUP084	Design of Single Spoke Resonators for Project X	cavity, linac, proton, ion	982
	L. Ristori, S. Barbanotti, M.S. Champion, M.H. Foley, I.G. Gonin, C.J. Grimm, T.N. Khabiboulline, N. Solyak, V.P. Yakovlev Fermilab, Batavia, USA
	Project X is based on a 3 GeV CW superconducting linac and is currently in the R&D phase awaiting CD-0 approval. The low-energy section of the Project X H-linac includes three types of super-conducting single spoke cavities operating at 325 MHz. SSR0 (26 cavities), SSR1 (18 cavities) and SSR2 (44 cavities) have a geometrical beta of = 0.11, 0.21 and 0.4 respectively. Single spoke cavities were selected for the linac in virtue of their higher r/Q. In this paper we present the decisions and analyses that lead to the final designs. Electro-magnetic and mechanical finite element analyses were performed with the purpose of optimizing the electro-magnetic design, minimizing frequency shifts due to Helium bath pressure fluctuations and providing a pressure rating for the resonators that allow their use in the cryomodules.

TUP085	Assumptions for the RF Losses in the 650 MHz Cavities of the Project X Linac	cavity, linac, factory, target	985
	A. Romanenko, L.D. Cooley, J.P. Ozelis, N. Solyak, V.P. Yakovlev Fermilab, Batavia, USA
	The requirements for the FNAL Project X cryogenic system depend on the dynamic heat loads of 650 MHz cavities. The heat load is in turn determined by quality factors of the cavities at the operating gradient. In this contribution we use the available experimental data to analyze quality factors achievable in 650 MHz linac cavities taking into account different RF losses contributions such as BCS resistance, residual resistance and a medium field Q-slope.

TUP102	Cryogenic RF Material Testing at SLAC	cavity, shielding, cryogenics, factory	1030
	J. Guo, D.W. Martin, S.G. Tantawi, C. Yoneda SLAC, Menlo Park, California, USA
	Funding: The work is supported by the US Department of Energy We have been developing an X-band cryogenic RF material testing system since 2005. By measuring the Q of a hemispherical cavity with the material sample at is flat interchangeable bottom, the system is capable to characterize the surface resistance of different materials at the temperature of 3-300K, as well as the quenching RF magnetic field of the superconducting samples at different temperatures. Using a SLAC X-band 50 MW klystron, the system can measure the quenching H-field of up to 300mT under current setup, with the possibility of further enhancement by changing the RF distribution configuration.

TUP106	Effect of Surface Flow on Topography in Niobium Electropolishing	cavity, SRF, superconductivity, cathode	1038
	M.J. Kelley, C.E. Reece JLAB, Newport News, Virginia, USA L. Zhao The College of William and Mary, Williamsburg, USA
	Funding: This work has been supported by U.S. DOE Contract No. DE-AC05-06OR23177 to Jefferson Lab Electropolishing (EP) is reliably delivering improved performance of multi-celled niobium SRF accelerator cavities, attributed to the smoother surface obtained. This superior leveling is a consequence of an etchant concentration gradient layer that arises in the HF-H2SO4 electrolyte adjacent to the niobium surface during polishing. Electrolyte circulation raises the prospect that fluid flow adjacent to the surface might affect the diffusion layer and impair EP performance. In this study, preliminary bench-top experiments with a moving electrode apparatus were conducted. We find that flow conditions approximating cavity EP show no effects attributable to depletion layer disruption.

TUP269	Design and Analysis of SRF Cavities for Pressure Vessel Code Compliance	cavity, SRF, electron, vacuum	1322
	C.M. Astefanous, J.P. Deacutis, D. Holmes, T. Schultheiss AES, Medford, NY, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA W. Xu BNL, Upton, Long Island, New York, USA
	Funding: This work was funded by Stony Brook University under contract number 52702. Advanced Energy Systems, Inc. is under contract to Stony Brook University to design and build a 704 MHz, high current, Superconducting RF (SRF) five cell cavity to be tested at Brookhaven National Laboratory. This cavity is being designed to the requirements of the SPL at CERN while also considering operation with electrons for a potential RHIC upgrade at Brookhaven. The β=1 cavity shape, developed by Brookhaven, is designed to accelerate 40 mA of protons at an accelerating field of 25 MV/m with a Q0 > 8·10⁹ at 2K while providing excellent HOM damping for potential electron applications. 10-CFR-851 states that all pressurized vessels on DOE sites must conform to applicable national consensus codes or, if they do not apply, provide an equivalent level of safety and protection. This paper presents how the 2007 ASME Boiler and Pressure Vessel Code Section VIII, Division 2 requirements can be used to satisfy the DOE pressure safety requirements for a non-code specified material (niobium) pressure vessel.

TUP270	RF and Structural Analysis of the 72.75 MHz QWR for the ATLAS Upgrade	cavity, cryomodule, coupling, cryogenics	1325
	T. Schultheiss, J. Rathke AES, Medford, NY, USA J.D. Fuerst, M.P. Kelly, P.N. Ostroumov ANL, Argonne, USA
	Funding: This work was supported by Argonne National Lab under contract # 0F-32381 & 0F32422 An energy upgrade to the heavy-ion accelerator ATLAS at Argonne Lab is progressing,. The plans include replacing split-ring cavities with high performance quarter wave resonators. The new 72.75 MHz resonators are designed for optimum ion velocity β=.077 and a record high accelerating voltage of 2.5 MV by modifying the top geometry and reducing the peak surface fields. This new cavity has a longer center conductor than the 10⁹ MHz cavities previously built by ANL with AES assistance, this and the other geometry changes add new engineering requirements to the design. This paper presents the engineering studies that were performed to resolve new issues. These studies include determining structural frequencies of the center conductor and stiffening methods, resonator frequency sensitivity to helium pressure fluctuations, and determining stress levels due to pressure and slow tuning. Evaluation of fast piezoelectric tuner frequency shift to tuner load was also performed and the local cavity shape was optimized based on these results. P.N. Ostroumov, et.al, “A New Atlas Efficiency and Intensity Upgrade Project,” SRF2009, tuppo016 ** P.N. Ostroumov, et.al., “Efficiency and Intensity Upgrade of the Atlas Facility,” LINAC 2010, MOP045

TUP271	CESR-type SRF Cavity - Meeting the ASME Pressure Vessel Criteria by Analysis	cavity, SRF, cryomodule, factory	1328
	T. Schultheiss, J. Rathke AES, Medford, NY, USA V. Ravindranath, J. Rose, S.K. Sharma BNL, Upton, Long Island, New York, USA
	Funding: This work is supported by BNL under contract #147322 Over a dozen CESR-B Type SRF cryomodules have been implemented in advanced accelerators around the world. The cryomodule incorporates a niobium cavity operating in liquid helium at approximately 1.2 bar and at 4.5 K, and therefore, is subjected to a differential pressure of 1.2 bar to the beam vacuum. Over the past few decades niobium RRR values have increased, as manufacturing processes have improved, resulting in higher purity niobium and improved thermal properties. Along with these increases may come a decrease of yield strength, therefore, prior designs such as CESR-B, must be evaluated at the newer strength levels when using the newer high purity niobium. In addition to this the DOE directive 10CFR851 requires all DOE laboratories to provide a level of safety equivalent to that of the ASME Boiler and Pressure Vessel codes. The goal of this work was to analyze the CESR-B Type cavity and compare the results to ASME pressure vessel criteria and where necessary modify the design to meet the code criteria.

TUP272	Analysis and Comparison to Test of AlMg3 Seals Near a SRF Cavity	cavity, SRF, linac, cryomodule	1331
	T. Schultheiss, C.M. Astefanous, M.D. Cole, D. Holmes, J. Rathke AES, Medford, NY, USA I. Ben-Zvi, D. Kayran, G.T. McIntyre, B. Sheehy, R. Than BNL, Upton, Long Island, New York, USA A. Burrill JLAB, Newport News, Virginia, USA
	The Energy Recovery Linac (ERL) presently under construction at Brookhaven National Laboratory is being developed as research and development towards eRHIC, an Electron-Heavy Ion Collider. The experimental 5-cell 703.75 MHz (ECX) cavity was recently evaluated at continuous field levels greater than 10 MV/m. These tests indicated stored energy limits of the cavity on the order of 75 joules. During design of the cavity the cold flange on one side was moved closer to the cavity to allow the cavity to fit into the available chemical processing chamber at Jefferson Laboratory. RF and thermal analysis of the AlMg3 seal region of the closer side indicate this to be the prime candidate limiting the fields. This work presents the analysis results and compares these results to test data.

WEOCS4	Integrated EM & Thermal Simulations with Upgraded VORPAL Software	HOM, simulation, cryogenics, plasma	1463
	D.N. Smithe, D. Karipides, P. Stoltz Tech-X, Boulder, Colorado, USA G. Cheng, H. Wang JLAB, Newport News, Virginia, USA
	Funding: This work supported by a DOE Phase II SBIR. Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.
	Slides WEOCS4 [0.996 MB]

WEODS3	CEBAF 200 kV Inverted Electron Gun	high-voltage, laser, electron, vacuum	1501
	J.M. Grames, P.A. Adderley, J. Clark, J. Hansknecht, M. Poelker, M.L. Stutzman, R. Suleiman, K.E.L. Surles-Law JLAB, Newport News, Virginia, USA M. BastaniNejad Old Dominion University, Norfolk, Virginia, USA J.L. McCarter UVa, Charlottesville, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In addition, DOE-HEP funds this work in support of the ILC R&D program. Two DC high voltage GaAs photoguns have been built at Jefferson Lab based on a compact inverted insulator design. One photogun provides the polarized electron beam at CEBAF and operates at 130 kV bias voltage. The other gun is used for high average current lifetime studies at a dedicated test facility and has been operated at bias voltage up to 225 kV. The advantages of higher DC voltage for CEBAF include reduced space-charge emittance growth and the potential for prolonged photocathode lifetime. However, a consequence of operating at higher voltages is the increased likelihood of field emission or breakdown, both of which are unacceptable. Highlights of the R&D studies leading toward a production 200keV GaAs photogun for CEBAF will be presented.
	Slides WEODS3 [1.360 MB]

WEP287	Field Emission Measurements from Niobium Electrodes	cathode, high-voltage, vacuum, SRF	2020
	M. BastaniNejad Old Dominion University, Norfolk, Virginia, USA P.A. Adderley, J. Clark, S. Covert, J. Hansknecht, C. Hernandez-Garcia, R.R. Mammei, M. Poelker JLAB, Newport News, Virginia, USA
	Increasing the operating voltage of a DC high voltage photogun serves to minimize space charge induced emittance growth and thereby preserve electron beam brightness, however, field emission from the photogun cathode electrode can pose significant problems: constant low level field emission degrades vacuum via electron stimulated desorption which in turn reduces photocathode yield through chemical poisoning and/or ion bombardment and high levels of field emission can damage the ceramic insulator. Niobium electrodes (single crystal, large grain and fine grain) were characterized using a DC high voltage field emission test stand at maximum voltage -225kV and electric field gradient > 10MV/m. Niobium electrodes appear to be superior to diamond-paste polished stainless steel electrodes.

Paper

Title

Other Keywords

Page

MOP042

Design of a Superconducting Photonic Band Gap Structure Cell

SRF, cavity, HOM, wakefield

178

E.I. Simakov
LANL, Los Alamos, New Mexico, USA
C.H. Boulware, T.L. Grimm
Niowave, Inc., Lansing, Michigan, USA

Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program.
We present a design of a superconducting photonic band gap (PBG) accelerator cell operating at 700 MHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. Using PBG structures in superconducting particle accelerators will allow moving forward to significantly higher beam luminosities and lead towards a completely new generation of colliders for high energy physics. We designed the superconducting PBG cell which incorporates higher order mode (HOM) couplers to conduct the HOMs filtered by the PBG structure out of the cryostat. The accelerator characteristics of the cell were evaluated numerically. A scaled prototype cell was fabricated out of copper at the higher frequency of 2.8 GHz and cold-tested. The 700 MHz niobium cell will be fabricated at Niowave, Inc. and tested for high gradient at Los Alamos in the near future.

TUP032

Development of 1.3 GHz Prototype Niobium Single Cell Superconducting Cavity Under IIFC Collaboration

cavity, vacuum, controls, electron

871

A. Puntambekar, M. Bagre, J. Dwivedi, P.D. Gupta, R.K. Gupta, S.C. Joshi, G.V. Kane, R.S. Sandha, S.D. Sharma, P. Shrivastava
RRCAT, Indore (M.P.), India
C.A. Cooper, M.H. Foley, T.N. Khabiboulline, C.S. Mishra, J.P. Ozelis, A.M. Rowe, G. Wu
Fermilab, Batavia, USA
V. Jain
IIT, Mumbai, India
D. Kanjilal, K.K. Mistri, P.N. Potukuchi, J. Sacharias
IUAC, New Delhi, India
V.C. Sahni
Homi Bhbha National Institute (HBNI), DAE, Mumbai, India

Under Indian Institutions Fermilab collaboration (IIFC), Raja Ramanna Centre for Advanced Technology (RRCAT) Indore, Inter University Accelerator Centre (IUAC) New Delhi and Fermi National Accelerator Laboratory (FNAL) have developed two prototype 1.3 GHz niobium single cell superconducting cavities. Development of forming tools, forming of half cells, machining of components, development of welding fixtures along with RF & vacuum qualification were carried out at RRCAT. The electron beam welding was carried out at IUAC. The fabricated prototype cavities were tested for RF and vacuum leak tightness up to 77 K at RRCAT before shipment to FNAL. Processing, consisting of CBP, EP, and heat treatment was carried out jointly by FNAL and Argonne National Laboratory in USA. Both the prototype cavities were tested at 2 K in the VTS facility at FNAL and have achieved the accelerating gradient of ~ 19 to 21 MV/m with Q > 1.5 ·10⁺¹⁰. This paper will report the developmental efforts carried out in tooling, forming, machining, welding & various qualification procedures adopted. The paper will also present the processing and the 2 K test results.

TUP046

Superconducting 72 MHz β=0.077 Quarter-wave Cavity for ATLAS

cavity, linac, ion, cathode

892

M.P. Kelly, Z.A. Conway, S.M. Gerbick, M. Kedzie, R.C. Murphy, P.N. Ostroumov, T. Reid
ANL, Argonne, USA

A 72 MHz superconducting (SC) niobium quarter-wave cavity (QWR) optimized for β=0.077 has been built and tested as part of a beam intensity upgrade of the ATLAS SC heavy-ion linac. The two-gap cavity, designed to accelerate ions over the velocity range 0.06<β<0.12 and provide 2.5 MV of accelerating voltage per cavity at T=4.5 Kelvin, is based on a highly optimized electromagnetic design to reduce surface electric and magnetic fields. Horizontal electropolishing on the complete cavity with the helium jacket, is similar to that performed on 1.3 GHz ILC-type cavities and is a first for a low-β TEM cavity. This development is part of a broader effort to demonstrate ~120 mT surface fields with Rs~5 nΩ in 2 K operation for low-β cavities with the aim of substantially reducing the footprint for future ion linacs. First rf cold test results show the highest accelerating gradients (13.4 MV/m, leff=βλ) and voltage/cavity (4.3 MV) achieved for this class of SC cavity.

TUP054

Mechanical Design of 56 MHz Superconducting RF Cavity for RHIC Collider

cavity, SRF, vacuum, resonance

907

C. Pai, I. Ben-Zvi, A. Burrill, X. Chang, G.T. McIntyre, R. Than, J.E. Tuozzolo, Q. Wu
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A 56 MHz Superconducting RF Cavity operating at 4.4K is being constructed for the RHIC collider. This cavity is a quarter wave resonator with beam transmission along the centreline. This cavity will increase collision luminosity by providing a large longitudinal bucket for stored bunches of RHIC ion beam. The major components of this assembly are the niobium cavity with the mechanical tuner, its titanium helium vessel and vacuum cryostat, the support system, and the ports for HOM and fundamental dampers. The cavity and its helium vessel must meet the ASME pressure vessel code and it must not be sensitive to frequency shift due to pressure fluctuations from the helium supply system. Frequency tuning achieved by a two stage mechanical tuner is required to meet performance parameters. This tuner mechanism pushes and pulls the tuning plate in the gap of niobium cavity. The tuner mechanism has two separate drive systems to provide both coarse and fine tuning capabilities. This paper discusses the design detail and how the design requirements are met.

TUP055

Design and Preliminary Test of the 1500 MHz NSLS-II Passive Superconducting RF Cavity

cavity, HOM, cryomodule, vacuum

910

J. Rose, W.K. Gash, B.N. Kosciuk, V. Ravindranath, S.K. Sharma, R. Sikora, N.A. Towne
BNL, Upton, Long Island, New York, USA
C.H. Boulware, T.L. Grimm, C. Krizmanich, B. Kuhlman, N. Miller, B. Siegel, M.J. Winowski
Niowave, Inc., Lansing, Michigan, USA

NSLS-II is a new ultra-bright 3 GeV 3rd generation synchrotron radiation light source. The performance goals require operation with a beam current of 500mA and a bunch current of at least 0.5mA. Ion clearing gaps are required to suppress ion effects on the beam. The natural bunch length of 3mm is planned to be lengthened by means of a third harmonic cavity in order to increase the Touschek limited lifetime. Earlier work described the design alternatives and the geometry selected for a copper prototype. We subsequently have iterated the design to lower the R/Q of the cavity and to increase the diameter of the beam pipe ferrite HOM dampers to reduce the wakefield heating. A niobium cavity and full cryomodule including LN2 shield, magnetic shield and insulating vacuum vessel have been fabricated and installed.

TUP084

Design of Single Spoke Resonators for Project X

cavity, linac, proton, ion

982

L. Ristori, S. Barbanotti, M.S. Champion, M.H. Foley, I.G. Gonin, C.J. Grimm, T.N. Khabiboulline, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, USA

Project X is based on a 3 GeV CW superconducting linac and is currently in the R&D phase awaiting CD-0 approval. The low-energy section of the Project X H-linac includes three types of super-conducting single spoke cavities operating at 325 MHz. SSR0 (26 cavities), SSR1 (18 cavities) and SSR2 (44 cavities) have a geometrical beta of = 0.11, 0.21 and 0.4 respectively. Single spoke cavities were selected for the linac in virtue of their higher r/Q. In this paper we present the decisions and analyses that lead to the final designs. Electro-magnetic and mechanical finite element analyses were performed with the purpose of optimizing the electro-magnetic design, minimizing frequency shifts due to Helium bath pressure fluctuations and providing a pressure rating for the resonators that allow their use in the cryomodules.

TUP085

Assumptions for the RF Losses in the 650 MHz Cavities of the Project X Linac

cavity, linac, factory, target

985

A. Romanenko, L.D. Cooley, J.P. Ozelis, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, USA

The requirements for the FNAL Project X cryogenic system depend on the dynamic heat loads of 650 MHz cavities. The heat load is in turn determined by quality factors of the cavities at the operating gradient. In this contribution we use the available experimental data to analyze quality factors achievable in 650 MHz linac cavities taking into account different RF losses contributions such as BCS resistance, residual resistance and a medium field Q-slope.

TUP102

Cryogenic RF Material Testing at SLAC

cavity, shielding, cryogenics, factory

1030

J. Guo, D.W. Martin, S.G. Tantawi, C. Yoneda
SLAC, Menlo Park, California, USA

Funding: The work is supported by the US Department of Energy
We have been developing an X-band cryogenic RF material testing system since 2005. By measuring the Q of a hemispherical cavity with the material sample at is flat interchangeable bottom, the system is capable to characterize the surface resistance of different materials at the temperature of 3-300K, as well as the quenching RF magnetic field of the superconducting samples at different temperatures. Using a SLAC X-band 50 MW klystron, the system can measure the quenching H-field of up to 300mT under current setup, with the possibility of further enhancement by changing the RF distribution configuration.

TUP106

Effect of Surface Flow on Topography in Niobium Electropolishing

cavity, SRF, superconductivity, cathode

1038

M.J. Kelley, C.E. Reece
JLAB, Newport News, Virginia, USA
L. Zhao
The College of William and Mary, Williamsburg, USA

Funding: This work has been supported by U.S. DOE Contract No. DE-AC05-06OR23177 to Jefferson Lab
Electropolishing (EP) is reliably delivering improved performance of multi-celled niobium SRF accelerator cavities, attributed to the smoother surface obtained. This superior leveling is a consequence of an etchant concentration gradient layer that arises in the HF-H2SO4 electrolyte adjacent to the niobium surface during polishing. Electrolyte circulation raises the prospect that fluid flow adjacent to the surface might affect the diffusion layer and impair EP performance. In this study, preliminary bench-top experiments with a moving electrode apparatus were conducted. We find that flow conditions approximating cavity EP show no effects attributable to depletion layer disruption.

TUP269

Design and Analysis of SRF Cavities for Pressure Vessel Code Compliance

cavity, SRF, electron, vacuum

1322

C.M. Astefanous, J.P. Deacutis, D. Holmes, T. Schultheiss
AES, Medford, NY, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA
W. Xu
BNL, Upton, Long Island, New York, USA

Funding: This work was funded by Stony Brook University under contract number 52702.
Advanced Energy Systems, Inc. is under contract to Stony Brook University to design and build a 704 MHz, high current, Superconducting RF (SRF) five cell cavity to be tested at Brookhaven National Laboratory. This cavity is being designed to the requirements of the SPL at CERN while also considering operation with electrons for a potential RHIC upgrade at Brookhaven. The β=1 cavity shape, developed by Brookhaven, is designed to accelerate 40 mA of protons at an accelerating field of 25 MV/m with a Q0 > 8·10⁹ at 2K while providing excellent HOM damping for potential electron applications. 10-CFR-851 states that all pressurized vessels on DOE sites must conform to applicable national consensus codes or, if they do not apply, provide an equivalent level of safety and protection. This paper presents how the 2007 ASME Boiler and Pressure Vessel Code Section VIII, Division 2 requirements can be used to satisfy the DOE pressure safety requirements for a non-code specified material (niobium) pressure vessel.

TUP270

RF and Structural Analysis of the 72.75 MHz QWR for the ATLAS Upgrade

cavity, cryomodule, coupling, cryogenics

1325

T. Schultheiss, J. Rathke
AES, Medford, NY, USA
J.D. Fuerst, M.P. Kelly, P.N. Ostroumov
ANL, Argonne, USA

Funding: This work was supported by Argonne National Lab under contract # 0F-32381 & 0F32422
An energy upgrade to the heavy-ion accelerator ATLAS at Argonne Lab is progressing*,**. The plans include replacing split-ring cavities with high performance quarter wave resonators. The new 72.75 MHz resonators are designed for optimum ion velocity β=.077 and a record high accelerating voltage of 2.5 MV by modifying the top geometry and reducing the peak surface fields. This new cavity has a longer center conductor than the 10⁹ MHz cavities previously built by ANL with AES assistance, this and the other geometry changes add new engineering requirements to the design. This paper presents the engineering studies that were performed to resolve new issues. These studies include determining structural frequencies of the center conductor and stiffening methods, resonator frequency sensitivity to helium pressure fluctuations, and determining stress levels due to pressure and slow tuning. Evaluation of fast piezoelectric tuner frequency shift to tuner load was also performed and the local cavity shape was optimized based on these results.
* P.N. Ostroumov, et.al, “A New Atlas Efficiency and Intensity Upgrade Project,” SRF2009, tuppo016
** P.N. Ostroumov, et.al., “Efficiency and Intensity Upgrade of the Atlas Facility,” LINAC 2010, MOP045

TUP271

CESR-type SRF Cavity - Meeting the ASME Pressure Vessel Criteria by Analysis

cavity, SRF, cryomodule, factory

1328

T. Schultheiss, J. Rathke
AES, Medford, NY, USA
V. Ravindranath, J. Rose, S.K. Sharma
BNL, Upton, Long Island, New York, USA

Funding: This work is supported by BNL under contract #147322
Over a dozen CESR-B Type SRF cryomodules have been implemented in advanced accelerators around the world. The cryomodule incorporates a niobium cavity operating in liquid helium at approximately 1.2 bar and at 4.5 K, and therefore, is subjected to a differential pressure of 1.2 bar to the beam vacuum. Over the past few decades niobium RRR values have increased, as manufacturing processes have improved, resulting in higher purity niobium and improved thermal properties. Along with these increases may come a decrease of yield strength, therefore, prior designs such as CESR-B, must be evaluated at the newer strength levels when using the newer high purity niobium. In addition to this the DOE directive 10CFR851 requires all DOE laboratories to provide a level of safety equivalent to that of the ASME Boiler and Pressure Vessel codes. The goal of this work was to analyze the CESR-B Type cavity and compare the results to ASME pressure vessel criteria and where necessary modify the design to meet the code criteria.

TUP272

Analysis and Comparison to Test of AlMg3 Seals Near a SRF Cavity

cavity, SRF, linac, cryomodule

1331

T. Schultheiss, C.M. Astefanous, M.D. Cole, D. Holmes, J. Rathke
AES, Medford, NY, USA
I. Ben-Zvi, D. Kayran, G.T. McIntyre, B. Sheehy, R. Than
BNL, Upton, Long Island, New York, USA
A. Burrill
JLAB, Newport News, Virginia, USA

The Energy Recovery Linac (ERL) presently under construction at Brookhaven National Laboratory is being developed as research and development towards eRHIC, an Electron-Heavy Ion Collider. The experimental 5-cell 703.75 MHz (ECX) cavity was recently evaluated at continuous field levels greater than 10 MV/m. These tests indicated stored energy limits of the cavity on the order of 75 joules. During design of the cavity the cold flange on one side was moved closer to the cavity to allow the cavity to fit into the available chemical processing chamber at Jefferson Laboratory. RF and thermal analysis of the AlMg3 seal region of the closer side indicate this to be the prime candidate limiting the fields. This work presents the analysis results and compares these results to test data.

WEOCS4

Integrated EM & Thermal Simulations with Upgraded VORPAL Software

HOM, simulation, cryogenics, plasma

1463

D.N. Smithe, D. Karipides, P. Stoltz
Tech-X, Boulder, Colorado, USA
G. Cheng, H. Wang
JLAB, Newport News, Virginia, USA

Funding: This work supported by a DOE Phase II SBIR.
Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.

Slides WEOCS4 [0.996 MB]

WEODS3

CEBAF 200 kV Inverted Electron Gun

high-voltage, laser, electron, vacuum

1501

J.M. Grames, P.A. Adderley, J. Clark, J. Hansknecht, M. Poelker, M.L. Stutzman, R. Suleiman, K.E.L. Surles-Law
JLAB, Newport News, Virginia, USA
M. BastaniNejad
Old Dominion University, Norfolk, Virginia, USA
J.L. McCarter
UVa, Charlottesville, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In addition, DOE-HEP funds this work in support of the ILC R&D program.
Two DC high voltage GaAs photoguns have been built at Jefferson Lab based on a compact inverted insulator design. One photogun provides the polarized electron beam at CEBAF and operates at 130 kV bias voltage. The other gun is used for high average current lifetime studies at a dedicated test facility and has been operated at bias voltage up to 225 kV. The advantages of higher DC voltage for CEBAF include reduced space-charge emittance growth and the potential for prolonged photocathode lifetime. However, a consequence of operating at higher voltages is the increased likelihood of field emission or breakdown, both of which are unacceptable. Highlights of the R&D studies leading toward a production 200keV GaAs photogun for CEBAF will be presented.

Slides WEODS3 [1.360 MB]

WEP287

Field Emission Measurements from Niobium Electrodes

cathode, high-voltage, vacuum, SRF

2020

M. BastaniNejad
Old Dominion University, Norfolk, Virginia, USA
P.A. Adderley, J. Clark, S. Covert, J. Hansknecht, C. Hernandez-Garcia, R.R. Mammei, M. Poelker
JLAB, Newport News, Virginia, USA

Increasing the operating voltage of a DC high voltage photogun serves to minimize space charge induced emittance growth and thereby preserve electron beam brightness, however, field emission from the photogun cathode electrode can pose significant problems: constant low level field emission degrades vacuum via electron stimulated desorption which in turn reduces photocathode yield through chemical poisoning and/or ion bombardment and high levels of field emission can damage the ceramic insulator. Niobium electrodes (single crystal, large grain and fine grain) were characterized using a DC high voltage field emission test stand at maximum voltage -225kV and electric field gradient > 10MV/m. Niobium electrodes appear to be superior to diamond-paste polished stainless steel electrodes.